الفهرس 
Bone AnatomyOnly 14 pages are availabe for public view
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Abstract
Malignant tumors are the second most common cause of death and are responsible for more than 12% of all deaths worldwide. Mortality rates and the success of therapeutic approaches depend mainly on the type of cancer and the presence of metastases.
Bone metastases are the most common malignant bone tumor. Skeletal involvement occurs in 30%–70% of all cancer patients. Detection of primary tumor and bone metastases is essential for optimal therapy.
The added value of FDG PET/CT over other diagnostic modalities lies in the fact that it allows non-invasive evaluation and accurate cancer staging throughout the body in a single examination.
PET/CT offers a unique hybrid imaging technique that combines the attenuation and morphologic detail of CT with the metabolic information from PET. These images can be fused to allow accurate co-registration of anatomic and functional data, and the combination of the two types of images leads to more assured anatomic localization of areas of increased metabolic activity.
Accurate anatomic localization of foci of increased metabolic activity can be difficult or impossible at stand alone PET, particularly in the abdomen and pelvis, which are characterized by a lack of reliable identifiable anatomic structures and variable physiological FDG uptake.
The characterization of malignant bone lesions with FDG PET via:
1) Evaluation of the signal intensity of foci on the basis of semiquantitative standardized uptake value measurements (greater than 2.5).
2) Visual assessment of signal intensity by means of comparison to physiologic structures such as the liver, bowel, and background soft tissue.
3) Visual assessment of the focality (focal or diffuse and single or mltiple) and location of each lesion.
Malignant bone lesion seen at PET-CT is characterized with activity that is much greater than that of the liver, (SUV>2.5), focal (not diffuse), away from sites of physiological uptake or showing higher uptake than underlying physiological structure as well as morphological disruptions seen at CT of same bone lesion (lytic, sclerotic or mixed lesions harboring soft tissue component, endosteal scalloping, cortical breakthrough, periosteal reaction, expansile appearance, or associated pathologic fracture ) .
So lesion with activity that is less than that of the liver, SUV<2.5 and diffuse with benign CT features can confidently be diagnosed as benign bone lesion.
An understanding of the principles of PET/CT and recognition of its limitations are important for the optimal use of this imaging modality.
In general, malignant lesions show 18F-FDG activity equal to or greater than liver activity, although benign entities like inflammatory lesions and hypermetabolic lesions may also show increased 18F-FDG uptake giving false positive FDG uptake results so visualization of the bone metastasis is difficult with stand alone PET.
False negative PET findings can result if bone lesions are either sclerotic nature or non FDG avid. High neighboring background activity can also obscure FDG uptake.
Lesions presenting on PET/CT as sites of increased uptake with normal CT findings (showing neither benign nor malignant changes) or presented by malignant CT findings with negative co-registered FDG PET images, can be categorized on PET/CT interpretation as inconclusive.
The PET and CT interpretations can be discordant. This poses a relatively frequent diagnostic dilemma when interpreting these examinations and proved to be a large impetus for deeper analysis (e.g. MRI and Biopsy).